Devices for mixing liquids to form solutions and/or emulsions and for dissolving and/or suspending gases and solids in liquids are known. In particular, devices of the type improved by the present invention are known which include an open-top tank and means extending downwardly through the open top to agitate the liquid in the tank to mix it with another material which may be in gaseous, liquid, or solid phase. Apparatus of this general type is disclosed in U.S. Pat. Nos. 2,651,582 and 2,787,448. A commercially available device of this type, known as the Cowle's Dissolver, comprises a hydraulic lift to raise and lower a motor driven shaft at the lower end of which various types of impellers may be removably secured for agitating liquids in an open-top tank into which the shaft and impeller are lowered by the hydraulic lift. Many different types of impellers are disclosed in the prior art among which are the devices described in U.S. Pat. Nos. 211,248, 1,354,489, 1,692,617, 2,201,947, 2,581,414, 2,697,589, 2,787,448, 2,918,264, 3,111,305, 3,318,248, 3,690,621. Devices are also known which comprise a tank having a generally rounded bottom in the center of which is an impeller driven from below as exemplified in U.S. Pat. Nos. 2,351,492, 2,665,853, 2,945,634, 3,009,656, 3,085,756 and 3,432,107. Pin mixers are also known as exemplified by U.S. Pat. Nos. 2,639,901 and 2,641,453 in which a disk is provided with a plurality of upwardly extending pins that rotate between downwardly extending pins on a cover for the mixing device.
All of the foregoing devices have serious deficiencies in producing mixtures of liquid with gasses, liquids or solids to produce solutions, emulsions, suspensions and the like, particularly when used in open-top tanks. Among other difficulties and disadvantages with impellers of the types known to the prior art are throwing of the liquid out of the tank, particularly when the impeller is raised to increase the size of the lower zone and decrease the size of the upper zone in the tank, slow and/or inadequate rate of dissolution of the solids in the liquid and lack of homogeniety in the mixture produced.
These difficulties and disadvantages have been overcome by the present invention.